There are no reproducible parameters to predict the duration of ventilation and length of stay for RSV-induced respiratory failure in previously healthy children. Tasker [1] found an alveolar–arterial gradient (AaDO2) > 400 with mean airway pressure (MAP) > 10 in the first 24 hours, and an AaDO2 > 300 with MAP > 10 over the subsequent 24 hours identified RSV-positive cases at risk of a prolonged stay. Another study found an AaDO2 > 253 in the first 24 hours to be the best predictor of developing severe disease with the need for a prolonged stay.

Data were collected from 118 cases of respiratory failure in a regional pediatric ICU over four RSV seasons. Forty-six were excluded with an alternative diagnosis; of the remaining 72 cases of bronchiolitis, 52 were RSV-positive (six not ventilated), and 20 were RSV-negative. Of the 46 ventilated RSV-positive, three had congenital heart disease, four had chronic lung disease, and one had been treated in a different unit prior to admission. Of the 20 RSV-negative cases, three had congenital heart and/or chronic lung disease. Both groups were assessed against Tasker's criteria and a multiple regression model used to identify predictive markers with length of ventilation as the dependent variable.

The median ages in the RSV-positive and RSV-negative groups were 0.13 (25th and 75th percentiles 0.05 and 0.23) and 0.11 (0.06 and 0.17), respectively. The length of ventilation was normally distributed with a mean (SD) of 110 (75) hours for the positive group and 110 (84) hours for the negative group. Mean (SD) lengths of stay of 7 (4) and 6 (4) days, respectively. The mean (SD) length of ventilation for those with AaDO2 > 400 within the first 24 hours was 127.7 (77.2) hours, AaDO2 > 300 for 24–48 hours was 127.2 (84.4) hours and AaDO2 > 253 in first24 hours was 122 (75.7) hours. Using Pearson's correlation the maximum MAP at 24 hours, 24–48 hours and the maximum ever were identified as potential predictive factors (P = 0.017, 0.037 and 0.038), for both the RSV-positive and RSV-negative groups. The maximum positive inspiratory pressure (PIP) at 24–48 hours may be predictive for RSV-positive (P = 0.079) and RSV-negative groups (P = 0.077). The multiple regression model found the maximum PIP between 24 and 48 hours in the combined group (RSV-positive and RSV-negative) to be an independent predictor of length of ventilation (P = 0.032), confirming the findings.

We have shown that the factors predicting severity of RSV-positive and RSV-negative respiratory failure are similar. We were unable to confirm the findings of previous studies suggesting that these are institute specific. In our institute a high MAP within the first 48 hours provides a predictive factor that can guide the clinician when talking to the parents and may help resource planning. A multicentre study in the UK is unlikely to yield more useful information.